Evidence exists that the retinal pigment epithelium (RPE) is one of the affected tissues in diabetic ocular disease. Specifically, the integrity of the blood-retinal barrier at the level of the RPE may be compromised. We are utilizing cultured human retinal pigment epithelium as a potential in vitro model system to study the effects of elevated hexose on these cells. RPE incubated with medium containing 30 mM galactose accumulates sugar alcohol (polyol) and loses myo-inositol, and these effects are reversed when an aldose reductase inhibitor is present in the high galactose medium. This suggests that aldose reductase may be active in RPE and that the polyol accumulation may contribute to impairment of RPE function in diabetes. the deficit does not appear to be at the level of the sodium, potassium-ATPase.